Field
The present disclosure relates generally to an oxygen saturation measuring apparatus and an oxygen saturation measuring method thereof, and for example, to an oxygen saturation measuring apparatus and an oxygen saturation measuring method thereof, for accurately measuring oxygen saturation in a mobile environment.
Description of Related Art
A conventional technology for measuring oxygen saturation includes 1) an invasive method of collecting arterial blood and directly analyzing oxygen saturation and 2) a non-invasive method of measuring light absorption when hemoglobin in blood is combined with oxygen and light absorption when hemoglobin is not combined with oxygen and measuring oxygen saturation using a ratio therebetween.
The method of collecting arterial blood and measuring oxygen saturation in the blood is capable of measuring a most accurate oxygen saturation value but has a problem in that a patient feels pain during blood collection and current oxygen saturation of blood of the patient is not capable of being acquired in real time because a predetermined time is taken to collect blood and to analyze an oxygen saturation value.
On the other hand, the non-invasive method of measuring oxygen saturation in blood does not cause pain to a patient by virtue of non-invasive measurement and is also capable of acquiring oxygen saturation in blood in real time and, thus, has been broadly used in environments outside a hospital as well as in clinical environments.
In detail, the non-invasive method of measuring oxygen saturation is a method of emitting red light and near infrared light on a sample, converting light that is not absorbed into the sample into an electrical signal, and measuring oxygen saturation. According to such a conventional technology, a peak and a valley need to be detected in a pulse according to each heartbeat in the time domain and, thus, the result is greatly affected by a signal to noise ratio (SNR) of a signal.
However, in environments outside a hospital, since an external light source such as sunlight or lighting is major influence and motion artifact due to motion such as arm motion or walking motion is a major influence, it is difficult to accurately detect a peak and a valley and, accordingly, there is a problem in that accurately of oxygen saturation is degraded.
In particular, when a reflection type sensor is used on a body surface like a wrist watch, it is difficult to ensure a robust contact state between a sensor and a skin surface as compared with a transmission type sensor used in the form of a clip at a finger and an SNR of a pulse wave signal measured by applying relatively large motion is remarkably lowered and, thus, detected peak and valley values are not accurate.
FIG. 1 is a diagram illustrating an example of a waveform of a pulse wave due to noise caused by an external light source or noise caused by contact inferiority between a finger and a sensor in a transmission type sensor (A left portion shows a signal of light in a near infrared wavelength and a right portion shows a signal of light in a red wavelength.). In this case, it is not possible to accurately detect peak and valley values and, thus, a serious error is caused in a calculated oxygen saturation value.
FIG. 2 is a diagram illustrating an example of a waveform of a pulse wave signal measured from a wrist-type device. When the pulse wave signal is measured in a state without motion, a pulse wave is clearly measured according to pulsation as illustrated in a left portion of FIG. 2 but, when there is wrist motion caused by walking, running, or the like, a motion artifact due to motion more largely overlaps than pulsation components and, thus, it is not possible to detect peak and valley values, as illustrated in a right portion of FIG. 2.
Accordingly, there is a need for a method of measuring accurate oxygen saturation even in an environment in which there is noise due to an external light source and noise due to motion.